What's more, a larger number of U.S. consumers aren't waiting until Black Friday to kick-start their holiday shopping campaign, even though ostensibly that's where the big discounts are.

Amex does say that Black Friday still resonates with shoppers, as 45% of U.S. adults will make a purchase that day. But the trend to start early is reducing the consumer firepower long associated with Black Friday. Amex notes the average Black Friday shopper will spend $398, about 25% less than in 2011.

The tracker also says that 43% of American consumers started their holiday shopping season not just before Black Friday, but before Halloween. That number is up from 35% last year.

What's behind the "early bird" mentality?

Apparently, an early start is on the wish list of shoppers and retailers. The former want to get out in front of the holidays for convenience, and the latter wants to fatten up the bottom line in October and the first three weeks of November -- not just after Black Friday and in December.

Plus, shoppers are getting more sophisticated about shopping, especially online and via mobile phones. Nowadays, it's commonplace for consumers to use a mobile phone or tablet computer to scan a bar code, or pop up some coupons for mobile purchases. So when consumers see a holiday gift deal, they strike no matter what month tops the calendar.

"An earlier start to the shopping season coupled with consumers' expectation of better deals and offers could explain the expected dip in average spending on Black Friday," offers Claire Bennett, an executive vice-president of loyalty & membership benefits at Amex. "Retailers are starting their holiday season earlier and earlier, and consumers are welcoming the chance to shop deals well before the Thanksgiving weekend."

Amex joins the list of analysts and data gathering outfits saying holiday spending will rise overall this year. The Amex tracker pegs the average spending totals on the high side - at $848 per U.S. consumer. Most estimates are coming in lower, at closer to $500, but there is little doubt Americans are digging deeper this holiday shopping season.

They're starting way earlier, too, which could be at the expense of future Black Fridays.